1. Field of the Invention
The present invention relates to an optical card reproducing apparatus for reproducing information recorded on an optical card with light, more specifically, to an optical card reproducing apparatus having a two-dimensional solid-state image sensing means comprising plural photoelectric conversion elements which are distributed two-dimensionally on a plane wherein any photoelectric conversion element can be specified by a first address in the X-direction and a second address in the Y-direction.
2. Statement of Related Art
In general, in a conventional way to read a sequence of pits recorded on an optical card, the card is moved in the direction of a track so as to scan a sequence of the pits one-dimensionally with a spot light, such as a laser beam, and the sequential data signals obtained by a detector are decoded.
As described in Japanese Patent Application Laid-Open No. 2-223064, in reproduction of data recorded by the self-clock modulation method, data is reproduced by reading each distance between data pits. A light beam emitted from a semiconductor laser is converged onto an optical card through an optical system, so that an optical spot is produced. The light beam is reflected by the surface of the optical card and detected by a photodiode.
The existence of pits can be detected by judging the amount of the reflected light, thus a pit detection signal is retrieved. In reproduction of signals recorded by the self-clock modulation method, the synchronizing signal is produced as a clock signal using a PLL or the like by extracting it from the pit detection signals. A decoded data is produced from the pit detection signals at the timing of the synchronizing signals. The pit detection signal is extracted sequentially from a recording medium moving in the direction of a track. Therefore, the detection rate of the pit detection signal depends on a driving speed of an electric motor for driving an optical card. Reading and writing of data are usually started when a specific pattern, so-called sync pattern, is detected from demodulation data.
Japanese Patent Application Laid-Open No. 2-141932 by the present applicant discloses an optical card reproducing apparatus wherein a plurality of tracks are read at the same time by applying one or more light beams to the plurality of tracks. In this optical card reproducing apparatus, data on each track is read by a detecting device or the like. One detecting device is assigned to each track and each detector works independently. Even in this optical card reproducing apparatus, as in that described above in Japanese Patent Application Laid-Open No. 2-223064, signals are detected in sequence and the detection rate also depends on a driving speed of an electric motor.
As described above, in a system wherein pits recorded on an optical card are scanned with a light beam by driving a card and detection signals are read sequentially, the driving of a card by an electric motor leads to a fluctuation in the moving speed of the card, and further leads to a fluctuation in the interval time between each pit detection signal. Therefore, even if pits were recorded at an accurate interval at the time of recording, fluctuations in the interval of pit signals would occur during reading signals due to fluctuations in driving speed. When such a fluctuation is too large or when a certain sudden signal fluctuation is added to the fluctuation in driving speed, an appropriate clock signal cannot be generated resulting in an inability to read data. Furthermore, failure in detection of a sync pattern results in an inability to determine when to start reading/writing data, thus it becomes unable to read/write data. That is, when there exists some dust or a defect on a track to be accessed, or when large fluctuations in signals exist due to fluctuations in speed because of back-and-forth movement of a card, a clock signal cannot be appropriately generated or a sync pattern cannot be detected. Thus there is a problem that it is impossible to read data.
In the case of a write-once medium such as an optical card, a decision is required whether the area to be recorded is a blank area or a used area before writing is carried out so as to assure that the data is going to be written in an area which is really blank. When an area turns out to be already previously written generally, the area will be skipped. Therefore, it is required to make an accurate decision of a blank (no-date is recorded) track.
If data was re-written by mistake in a recorded area (that is, duplication occurs in writing) in a writing process, it would become impossible not only to read the data recorded later but also the previously recorded data. Moreover, in a reading process, it is wasteful to decode duplicated signals unless duplication is judged.
As described above, in conventional technologies, pits recorded on an optical card are scanned with a light beam to read the pit signals sequentially. During this process for reading the signals sequentially, there is some probability that some disturbance causes wrong decision that a recorded track is taken as a blank track (no-data track), or that a duplicated track is taken as a normal track to make useless and inaccurate decoding.